feat(cli): add langgraph deploy logs subcommand (#7100)

Add a `langgraph deploy logs` subcommand to fetch build and
deploy/server logs from LangSmith deployments.

## Changes

- **`host_backend.py`**: Add `get_build_logs()` and `get_deploy_logs()`
methods, plus `langsmith_url` support.
- **`helpers.py`** (new): Log formatting (`format_log_entry`,
`format_timestamp`, `level_fg`) and resolution helpers
(`resolve_deployment_id`).

## Usage

```bash
# Deploy logs (latest 10)
langgraph deploy logs --deployment-id <id> --limit 10

# Error logs by name
langgraph deploy logs --name gtm-agent --level ERROR

# Build logs
langgraph deploy logs --deployment-id <id> --type build

# Tail logs (Ctrl+C to stop)
langgraph deploy logs --name gtm-agent --follow
```

## Tests

56 unit tests passing covering host backend methods, log formatting, and
helper functions.

---------

Co-authored-by: hari-dhanushkodi <hari@langchain.dev>

libs/cli/langgraph_cli/host_backend.py

@@ -19,7 +19,12 @@ class HostBackendError(click.ClickException):
 class HostBackendClient:
     """Minimal JSON HTTP client for the host backend deployment service."""
 
-    def __init__(self, base_url: str, api_key: str, tenant_id: str | None = None):
+    def __init__(
+        self,
+        base_url: str,
+        api_key: str,
+        tenant_id: str | None = None,
+    ):
         if not base_url:
             raise click.UsageError("Host backend URL is required")
         transport = httpx.HTTPTransport(retries=3)
@@ -30,7 +35,6 @@ class HostBackendClient:
         if tenant_id:
             headers["X-Tenant-ID"] = tenant_id
         self._base_url = base_url.rstrip("/")
-        self._api_key = api_key
         self._client = httpx.Client(
             base_url=self._base_url,
             headers=headers,
@@ -116,3 +120,24 @@ class HostBackendClient:
             "GET",
             f"/v2/deployments/{deployment_id}/revisions/{revision_id}",
         )
+
+    def get_build_logs(
+        self, project_id: str, revision_id: str, payload: dict[str, Any]
+    ) -> Any:
+        return self._request(
+            "POST",
+            f"/v1/projects/{project_id}/revisions/{revision_id}/build_logs",
+            payload,
+        )
+
+    def get_deploy_logs(
+        self,
+        project_id: str,
+        payload: dict[str, Any],
+        revision_id: str | None = None,
+    ) -> Any:
+        if revision_id:
+            path = f"/v1/projects/{project_id}/revisions/{revision_id}/deploy_logs"
+        else:
+            path = f"/v1/projects/{project_id}/deploy_logs"
+        return self._request("POST", path, payload)